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-4x+y=4 2x+2y=13

Guest Feb 28, 2017
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 #1
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-4x+y=4

2x+2y=13

 

\(\begin{array}{|lrcll|} \hline (1) & -4x+y &=& 4 \\ & y = 4+4x \\ (2) & 2x+2y &=& 13 \\ & 2x+2[4+4x]&=& 13 \\ & 2x+8+8x &=& 13 \\ & 10x+8&=& 13 \\ & 10x&=& 13 -8 \\ & 10x&=& 5 \\ & x&=& \frac{5}{10} \\ & x&=& \frac12 \\ & \mathbf{x} & \mathbf{=} & \mathbf{0.5} \\\\ & y &=& 4+4x \\ & y &=& 4+4\cdot {\frac12} \\ & y &=& 4+2 \\ & \mathbf{y} & \mathbf{=} & \mathbf{6} \\ \hline \end{array}\)

 

laugh

heureka  Feb 28, 2017
 #2
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-4x+y=4 (1)             -4x+y=4          (1)

2x+2y=13 (2)             4x+4y=26        (3)    

 

We add equations 1 and 3  ,and we get :5y=30=>y=6

We replace y=6 to the equation 1: -4x+6=4=>4x=2=>x=1/2

Guest Feb 28, 2017

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